Passing variables (locals) into a partial when rendering a partial from Deface

Question

I have a deface declaration, that adds a partial to every page just above </body>.

Deface::Override.new(
  :virtual_path => 'spree/layouts/spree_application',
  :name => 'add_piwik_tracking_tag_to_layout',
  :insert_bottom => "[data-hook='body']",
  :partial => 'spree/piwik')

The partial needs some variables. An example is a local or helper method:

_paq.push(['setSiteId', <%= piwik_site_id %>]);

or an instance variable:

_paq.push(['setSiteId', <%= @piwik_site_id %>]);

or entirely without variables:

_paq.push(['setSiteId', <%= Spree::Config.preferred_piwik_id %>]);

Is there any way to pass them along from the Deface::Override.new()?

I am trying to avoid three potentially bad patterns, especially since this piwik_site_id is one of many variables being passed in:

• Opening the application_helper from within my gem and insert a helper-method.
• Opening the ApplicationController and set a @piwik_site_id there. Setting this on every controller, for every action and each template.

I'd prefer to not have to pollute the controllers of the application that have this gem available.